The fuel can be classified into solid fuel, liquid fuel and gas fuel according to its form; it also can be classified into fossil fuel, biological fuel and nuclear fuel according to its type. Wherein, the liquid fuel includes crude oil and petroleum product, light diesel oil, heavy oil, gasoline, kerosene, coal tar, shale oil, synthetic oil, coal liquefaction oil, alcohol fuel and other liquid fuels.
Demand on energy is increasing with rapid development of world's economic, and energy problem has attracted more and more attentions from all aspects. Although fossil energy dominates at the present, coal, petroleum, natural gas and other mineral fuel resources are gradually exhausted due to serious exploration. From the nineties of the 20th century, under promotion of agricultural development, energy safety, climate change, environmental protection, etc., more and more countries actively participate in development of biological liquid fuel industry.
The biological liquid fuel is diverse in raw material resource, production technical route and product. Wherein, the biomass resource include lignocelluloses, starch, sugar, oil and grease of animal, plant and microorganism, etc., and the main product includes fuel ethanol, biological diesel oil, biological oil, catalytic hydrogenation biological diesel oil, biological methane, biological methanol, biological dimethyl ether, biological hydrogen, etc. The first generation of biological liquid fuel mainly includes fuel ethanol using starch and sugar from cane, corn, potato, etc. as raw material and biological diesel oil using grease as raw material. These products have long-term industrial application experience and comparatively mature technology. These products have good compatibility with the existing vehicle fuel and engine, and large-scale commercial production and application are realized. However, the energy crop which is adopted to develop the biological liquid fuel has remarkable problems of pushing up the costs of agricultural products and foods and threatening safety of grains, etc.
In the recent years, international biological liquid fuel technology and industry is in stage of upgrading and transforming to non-grain raw material, and novel biological liquid fuel using cellulose-like biomass as raw material is greatly developed. Owing to shortcomings of complex conversion, high investment cost, low utilization rate, low ethanol yield, etc. of cellulose raw material, the industrial and commercial applications of cellulose ethanol technology are still in trouble. At the same time, other various novel biological liquid fuels are limited as their immature production technologies and remarkable high production costs compared with gasoline, diesel oil and other petroleum fuels.
Dialkyl carbonate, called carbonic acid dialkyl ester as well, it includes alkoxy and carbonyl in the molecule which is capable to react with a plurality of alcohols, phenols, amines and esters. The dialkyl carbonate is an organic compound which has extremely wide application, high industrial application value and market prospect. The main process for producing the dialkyl carbonate includes phosgene synthesis, oxidative carbonylation, ester exchange, etc. The phosgene synthesis is generally adopted by the conventional industrial production of dialkyl carbonate, since the phosgene and intermediate product of the process are hyper-toxic materials, the byproduct has strong corrosion, the process has caused serious pollution of the environment and is gradually replaced by methanol oxidative carbonylation.
CN101234965B discloses a method for producing dialkyl carbonate. The invention performed a liquid-phase oxidative carbonylation reaction using a catalytic system consisting of an organic halogenated metallic catalyst and at least one catalysis promoter containing nitrogen atom in the presence of alcohol, carbon monoxide and oxygen to produce dialkyl carbonate. Though the method reduces corrosion on the reactor to a certain degree, shortcomings of high price, low conversion rate and selectivity of the catalyst still exist.
As a technology of generating a new ester by exchanging acyl between an ester and another fatty acid, alcohol or ester under a certain condition, the ester exchange technology had many advantages such as wide range of catalyst, moderate reacting condition, easy control of the process, high conversion rate, high quality of the product, etc. CN1699328A discloses a method for preparing dialkyl carbonate; it adopts dimethyl carbonate which is a green chemical raw material and with performance of clean, non-toxic and environmental-friendly to react with aliphatic monohydric alcohol to synthesize dialkyl ester. The method is carried out under moderate reacting conditions; in particular it is able to be produced by renewable biomass resource and is free from three-waste pollution in the producing process. However, the ester exchange reaction uses alcoholate or hydroxide of alkali metals or alkaline-earth metals, alkali carbonate, alkaline-earth carbonate, organic tin, organic zinc or alkaline resin as catalyst, the reacting rate of the process is low and the activity and selectivity is limited.
Besides dimethyl carbonate, cyclic carbonate can also be adopted as initial raw material to prepare dialkyl carbonates. CN102464587A discloses a method for preparing small molecular dialkyl carbonate by ester exchange; the invention adopts cyclic carbonate (such as ethylene carbonate, propylene carbonate and glycerol carbonate) and small molecular alcohol as raw materials and performs the reaction under normal pressure or reduced pressure in the presence of catalyst to prepare the dialkyl carbonate. The method has the advantages of moderate reacting condition, easy separation of catalyst, etc., and with the value of practical application.
Furthermore, furfuryl alcohol is an important organic chemical raw material and with very wide use. At present, it is mainly used for synthesis of resin with various functions, cold-resistant plasticizer, fiber, rubber and pharmaceutical, etc, it can also be used as solvent and rocket fuel, etc. Furfuryl alcohol is mainly obtained by catalytic hydrogenation of furfural, while furfural as the raw material can be obtained by cheap agricultural production. Two-thirds of the produced furfural in the world is used to produce furfuryl alcohol, and China is one of the countries with the most yield of furfural, and the annual output is about 100 thousands. While the furfural which used for the production of furfuryl alcohol only accounts for only about 5% of the total output, and 80% of the furfural is used for cheap exports. Therefore using of carbonate and alcohol which are abundant, green and cheap to develop liquid fuel with economic value and social benefit has important significance.
The present invention adopts dimethyl carbonate or cyclic carbonate which is produced by taking agricultural and forestry wastes as raw material as raw material for producing a liquid fuel, which participates in ester exchange reaction with monohydric alcohol or furfuryl alcohol to produce a series of carbonate products, such as ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, high carbon alcohol carbonate, etc. These products are free from toxicity, biodegradable and environmental-friendly, they contain the same carbons with gasoline, diesel oil and kerosene, so they have similar burning calorific value with them. In addition, owing to their special chemical structures, these products are more excellent than fossil-based liquid fuels in performance of lubrication, discharge, noise reduction, volatility, safety, environmental friendliness, etc., and they are also more excellent than biological liquid fuels in performance of low temperature, sealing material compatibility, thermal and oxidizing stabilities, corrosiveness, cost, etc. The liquid fuels are capable of effectively inhibiting corrosion and abrasion of equipment so as to prolong service lives of engine and metal parts. The novel liquid fuels are not reported in the international field at the present time.